Frequency changing apparatus



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Patented Feb. 29, 1944 FREQUENCY CHAN GING APPARATUS Francois JosephGerard van den Bosch, East Croydon, England, assignor to Vacuum-ScienceProducts Limited, London, England, a British ompany Original applicationMay 20, 1940, Serial No. 336,308. Divided and this application May 15,1942, Serial No. 443,154. In Great Britain May 4 Claims. (01. 250-20)This application is a division of my co-pending United Statesapplication No. 336,308, filed May 20, 1940, Patent No. 2,295,919,granted September 15, 1942, for improvements in Electron dischargedevices.

This invention relates to electron discharge devices adapted to operateas frequency-changing apparatus, and of the kind comprising an electrodeassembly having one or more electrodes employed for the purpose ofproducing a secondary electron emission inorder to obtain electronmultiplication. Usually, such electron multiplication assembly comprisesa primary cathode, one or more secondary cathodes and a collectorenclosed in an envelope and so arranged that electrons emitted by theprimary cathode are caused to impinge on the secondary cathode andliberate other electrons which impinge on the next secondary cathode,when more than one, and so on in succession to the collector.

According to the present invention a homodyne or frequency-changingapparatus comprises an electron discharge device having a thermioniccathode structure, two electrode assemblages associated with saidstructure, one of which is adapted to eiTect electron multiplication,means-associated with the other electrode assemblage for generating alocal oscillation, means for applying said oscillations to the firstsaid electrode assemblage, and means for applying a received signal alsoto the electrode assemblage whereby the received signal and localoscillations are mixed and amplified by the electron multiplication. Thefirst said electrode assemblage includes one or more secondary cathodes,two control electrodes and a collector anode, and the local oscillationsare applied to one of said electrodes, while the output from a radioreceiver is connected to the other control electrode.

The following is a'desc'ription of two forms of electron-dischargedevice suitable for use in the invention, and the electric circuit to beemployed therewith, reference being made to the accompanying drawing, inwhich- Figure 1 is a section through the electron-discharge device,showing the disposition of the various electrodes; I

Figure 2 is a diagrammatic view showing the manner in which theelectrodes are connected with the external circuits, and

Figure 3 shows an alternative form of thermionic cathode structure.

Referring to Figure 1 of the drawing, the 9311 119919 ll9ll$ comp i es e1 2 953 1 tu I? 11? ing an enlarged disc-like part II at one end. Theouter surface of this disc-like part is provided with a coating 28freely emitting electrons, such as a coating of barium oxide orstrontium oxide, and constitutes the cathode element of the electronmultiplier assembly. The electron emission from this cathode element iscontrolled by two grid electrodes l2 and I3 between'which there isprovided another electrode M in the form of aplate with a singleaperture through which the electrons are directed towards a secondarycathode I5. The secondary cathode I5 is an apertured electrodeconsisting ofa perforated plate, for instance, as described in thespecification of United States application No. 276,883, filed June 1,1939, Patent No. 2,254,- 128 granted August 26, 1941, but it mayalternatively be constituted by a wire grid or mesh. Other secondarycathodes similar to the secondary cathode 15 are provided, as indicatedat l6, l1, l8 and IS with a final secondary cathode 29 of disc form anda collector electrode 2| in the form of a grid interposed between thesecondary cathodes l9 and 2B. The secondary cathodes I8, l1, l8 and H]are each provided with an auxiliary electrode 22 to the front, asdescribed in the specification of United States application No. 326,813,filed March 29, 1940,

' Patent No. 2,285,848, granted June 9, 1942, and

connected electrically to the secondary cathode.

The tube I0 also has a second emissive coating 29 surrounded by acylindrical grid electrode 23 and a cylindrical anode 24 togetherconstituting a thermionic triode.

' A heating element 9 is provided within the tube 10 for indirectlyheating the tube and thus the cathode elements provided by the emissivecoatings on the tube. It is convenient to operate the cathode elementproviding the emission for electron multiplication at a lower tempera- Iture than the other cathode element, so that the heater preferably doesnot extend fully to the disc-like part II. For instance, the heater maybe arranged to lie within the tube 10 only adjacent that part which hasthe emissive coating for the triode assembly.

Around this triode assembly there is provided a cylindrical screen '25formed of a wire grid or mesh. This screen has an end member 26 havingan opening 21 in which the disc-like cathode element H of the multiplierassembly is located. The disc-like cathode element Il may be a close fitin the opening 21 and the screen is electrical- 1:! connected t t t matei! 9? the c thod trut ture. The cylindrical screen 25 may be formed by ametal tube instead of a grid or mesh.

One application of this electron-discharge de vice is as infrequency-changing apparatus, for instance in a radio receiver of thesuper-heterodyne type. In this case the thermionic triode assembly isconnected with an external circuit indicated at 30 in known manner forproducing,

These local with the triode, local oscillations. oscillations are fed tothe control electrode H! of the electron multiplier assembly and to thecontrol electrode I2 the incoming signals are applied direct or througha preselecting amplifier 3i. A mixing of the local oscillations andapplied signals is thus obtained and subsequent amplification isproduced through the. several multiplier stages of the electronmultiplier assembly. Progressively increasing potentials positive withrespect to the cathode element It are applied, to, the accelerator Hi,the secondary cathodes l5, H5, l1, l8, l9 and 2B and the collector 2|through the resistance potentiometer 35. The amplified output atintermediate frequency may thus .be applied to a tuned intermediatefrequency circuit 32 from the collector electrode 2| and utilised in anyknown manner for the reproduction of the signals. Thus, the intermediatefrequency signals from the circuits 32 may be applied to a detector 33,followed by an output signal. amplifier 34. The electron-dischargedevice may similarly be used in a homodyne circuit,

The electron multiplier assembly is provided with operating potentialsin known manner in that the secondary cathodes I to 2B and the collector2| are provided with progressively increasing positive potentials withrespect to the cathode tube It and the electrode M is also operated at apotential which is positive with respect to the cathode tube H] butgenerally lower than that of the first secondary cathode l5.

It is to be understood that the invention is not restricted to thespecific construction hereinbefore described with reference to Figure 1.For instance, a plurality of additional electron assemblies may beemployed having cathode elements spaced apart lengthwise of the tube Illand comprising two or more electrodes.

In the modification shown in Figure 3 the tube i0 is extended and has anadditional coating 36 freely emitting electrons, around which there ismounted a tubular anode 31, to form a thermionic diode. In this case thecylindrical screen 25 is extended to surround the diode and a metal disc38 is provided across this screen between the diode assembly and thetriode assembly.

In Figure 3 a modification of the metallic end member 26 is shown inwhich this member is formed with a small opening 21 through which thetube H! passes with the disc-like element ll situated above this endmember. In this case a short tube 3.9 is provided around the disclikeelement l I and is secured to theend member 26 of the screen;

I claim:

1. A homodyne Or frequency changing apparatus comprising an electrondischarge device having two electrode assemblages, a primary cathodestructure common to both said assemblages, an anode in each saidassemblage, so arranged with respect to said cathode as to produce twoseparate streams of electrons, at least one secondary electron emittingelectrode in one of said assemblages, means for applying a potentialthereto for producing electron multiplication, an electric circuitcoupled with the other assemblage and adapted to generate localoscillation', means for applying said oscillations to the stream ofelectrons to be multiplied, and means for applying a received signalalso to that stream.

2. A homodyne or frequency-changing apparatus comprisingan electrondischarge device,

two electrode assemblages, one of which assemblages is adapted to effectelectron multiplication and includes two. control electrodes, at leastone secondary cathode, and a collector electrode, means associated withthe other electrode assemblage for generating local. oscillations, meansfor applying said oscillations to one ofsaid control electrodes in. thefirst said assemblage, and means for applying areceived signalto theother electrode of that assemblage.

3. A homodyne or rrequencyrchanging apparatus comprising an electrondischarge device having two electrode assemblages, a primary cathodestructure common to both said assemblages, an anode in each saidassemblage. so arranged with respect to cathode as to produce twoseparate streams of electrons, one of which assemblages is adapted toeffect electron multiplicationin the stream with which it is associated,and includes two control electrodes, at least one secondary cathode andthe aforesaid anode, means associated with the other electrodeassemblage for generating local oscillations, means for applying saidoscillations to one of said control electrodes of the first assemblage,and a radio receiver connected with the other control electrode forapplying a received signal thereto.

4. An electron discharge device having two electrode assemblages, aprimary cathode structure common to both said assemblages, and an anodein each said. assemblage so arranged with respect to the cathode astoproduce two separate streams of electrons, one of which electrodeassemblages also includes a secondary cathode, and is adapted to effectelectron multiplication, the other of which electrode assemblages isadapted for operation other than by electron multiplication, circuitmeans connected with the second electrode assemblage for producingtherewith a local oscillation, means for feeding the local oscillationto one of the-control electrodes of the first assemblage, means'forapplying received signals to the other of said control electrodes,whereby said signals and said local oscillations are combined andamplified in the first said electrode assemblage, and means forextracting an output from the anode of the first said assemblage.

FRANCOIS JOSEPH GERARD VAN DEN bOEZCH.

